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  • 1 Post By Ronald Roe

Thread: for/in

  1. #1
    Senior Member
    Join Date
    Apr 2016
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    10 times


    the following piece of code is from Mozilla

    var obj = {a: 1, b: 2, c: 3};

    for (var prop in obj) {
    console.log('obj.' + prop, '=', obj[prop]);

    // Output:
    // "obj.a = 1"
    // "obj.b = 2"
    // "obj.c = 3"

    what I'm wondering is how can prop mean both the property name and the value?


  3. #2
    Senior Member
    Join Date
    Apr 2016
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    and shouldn't there be an equals sign in the first statement "var = prop in object" instead of "var prop in object"?

  4. #3
    Senior Member Ronald Roe's Avatar
    Join Date
    Mar 2011
    Oklahoma City
    Member #
    959 times
    This is one of those weird ones. So, you're going to run this on an object.

    What it's basically saying is "for each property in this object, do this stuff".

    Prop isn't meaning both, what they're doing is saying the property of the object. Object properties can be accessed either with dot notation:


    ... or with bracket notation:


    Both of those would return the value of the property. The difference between them is that you can't pass a variable for a property with dot notation.

    Finally, no, there shouldn't be an equal sign. This is because "in obj" is not the value of prop. Prop is the name of the property of the object being referenced for that iteration of the loop.
    busso likes this.
    Ron Roe
    Web Developer
    "If every app were designed using the same design template, oh wait...Bootstrap."

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